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PubMed2002

The regulation of nitrate and ammonium transport systems in plants.

Inorganic nitrogen concentrations in soil solutions vary across several orders of magnitude among different soils and as a result of seasonal changes. In order to respond to this heterogeneity, plants have evolved mechanisms to regulate and influx. In addition, efflux analysis using (13)N has revealed that there is a co-ordinated regulation of all component fluxes within the root, including biochemical fluxes. Physiological studies have demonstrated the presence of two high-affinity transporter systems (HATS) for and one HATS for in roots of higher plants. By contrast, in Arabidopsis thaliana there exist seven members of the NRT2 family encoding putative HATS for and five members of the AMT1 family encoding putative HATS for. The induction of high-affinity transport and Nrt2.1 and Nrt2.2 expression occur in response to the provision of, while down-regulation of these genes appear to be due to the effects of glutamine. High-affinity transport and AMT1.1 expression also appear to be subject to down-regulation by glutamine. In addition, there is evidence that accumulated and may act post-transcriptionally on transporter function. The present challenge is to resolve the functions of all of these genes. In Aspergillus nidulans and Chlamydomonas reinhardtii there are but two high-affinity transporters and these appear to have undergone kinetic differentiation that permits a greater efficiency of absorption over the wide range of concentration normally found in nature. Such kinetic differentiation may also have occurred among higher plant transporters. The characterization of transporter function in higher plants is currently being inferred from patterns of gene expression in roots and shoots, as well as through studies of heterologous expression systems and knockout mutants.

Anion Transport Proteins↗
PubMedDate not supplied

[Tooth transplantation].

In the light of the thesis of J. Thibault, the authors suggest, in association with transplantation of wisdom tooth buds into the alveolus of the first molar, a technique consisting of placing the graft in its pre-eruptive position, removing in a block the bud, the gubernaculum and the sub-jacent gingival mucosa. Under these conditions, eruption occurs at the same time as development of the roots, which represents the most physiological solution. At the same time as formation of the root, the authors noted a paradoxal rhizalysis, hypercementosis resulting in ankylosis and conservation of vitality. In addition, almost all the teeth transplanted proved to be highly vulnerable to caries.

Female↗
PubMed2006

[Glycinebetaine applied through roots protects the photosynthetic apparatus of tobacco seedlings under water stress].

Two tobacco (Nicotiana tabacum L.) cultivars (DHJ5210 and ZY100) with different drought tolerance were used to study the photosynthetic response to different water stress and the effects of glycinebetaine applied through roots on photosynthetic capacity. The physiological mechanisms of the improvement of tobacco photosynthesis by glycinebetaine applied through roots were analyzed. The results indicated that photosynthetic apparatus of tobacco leaves were more brittle and damaged by water stress, accompanied by negative changes of RWC (Fig. 2), chlorophyll content (Fig. 3), PSII photochemistry efficiency (Fig. 4), activity of Hill reaction (Fig. 5) and ATPase (Fig. 6), and the damage was more serious to ZY100 (drought sensitive cultivar) than DHJ5210 (drought resistant cultivar) under the same stress condition. Glycinebetaine applied through roots could be absorbed by tobacco roots and then accumulated in leaves (Fig. 1), which alleviated the decrease in photosynthetic variables of two cultivars and the improvement was more significant on ZY100 than DHJ5210. The positive function of glycinebetaine might be involved in its protective effect on antioxidant enzymes (Fig. 8), chloroplast protein and thylakoid membrane (Fig. 7).

Adaptation, Physiological↗
PubMed2004

An auxin-inducible gene from loblolly pine (Pinus taeda L.) is differentially expressed in mature and juvenile-phase shoots and encodes a putative transmembrane protein.

We have isolated a gene from loblolly pine, 5NG4, that is highly and specifically induced by auxin in juvenile loblolly pine shoots prior to adventitious root formation, but substantially down-regulated in physiologically mature shoots that are adventitious rooting incompetent. 5NG4 was highly auxin-induced in roots, stems and hypocotyls, organs that can form either lateral or adventitious roots following an auxin treatment, but was not induced to the same level in needles and cotyledons, organs that do not form roots. The deduced amino acid sequence shows homology to the MtN21 nodulin gene from Medicago truncatula. The expression pattern of 5NG4 and its homology to a protein from Medicago involved in a root-related process suggest a possible role for this gene in adventitious root formation. Homology searches also identified similar proteins in Arabidopsis thaliana and Oryza sativa. High conservation across these evolutionarily distant species suggests essential functions in plant growth and development. A 38-member family of genes homologous to 5NG4 was identified in the A. thaliana genome. The physiological significance of this redundancy is most likely associated with functional divergence and/or expression specificity of the different family members. The exact biochemical function of the gene is still unknown, but sequence and structure predictions and 5NG4::GFP fusion protein localizations indicate it is a transmembrane protein with a possible transport function.

Amino Acid Sequence↗
PubMed1985

An investigation of the dorsal root reflex using an in vitro preparation of the hamster spinal cord.

A detailed description is given of an hemisected spinal cord preparation from adult golden hamsters and this preparation has been used to investigate the physiology of the dorsal root reflex. In addition to antidromic reflex discharges which could be recorded from lumbar dorsal roots following stimulation of adjacent dorsal roots or the dorsal columns, spontaneous firing was also recorded from the dorsal roots. This activity reached a peak at 27 degrees C and was abolished at temperatures above 35 degrees C. Both the evoked and the spontaneous dorsal root activity were demonstrated to be travelling antidromically along the dorsal roots out of the cord, and replacement of the calcium in the bathing medium by manganese showed them to be of synaptic origin. Stimulation of a lumbar dorsal root was found to evoke a reflex in up to 4 adjacent spinal segments in both rostral and caudal directions, and a period of depressed activity was demonstrated following both evoked and spontaneous discharges. A time-locked relationship was found between the dorsal root reflex and the slow dorsal horn potential recorded from within the spinal cord.

Animals↗
PubMed2005

Physiological changes of Fagus sylvatica seedlings infected with Phytophthora citricola and the contribution of its elicitin "citricolin" to pathogenesis.

Beech seedlings were infected with the root rot pathogen Phytophthora citricola to study its impact on leaf physiology and water status. Net photosynthesis rate decreased two days after inoculation in infected seedlings. In contrast, electron quantum yield of photosystem II, leaf water potential, and total water consumption were only slightly impaired until 6 dpi. At the same time, wilt symptoms occurred on leaves. These results indicate the involvement of a mobile signal triggering the early changes in leaf physiology by root infection. As the elicitin gene of P. citricola was induced during root infection, we purified and characterised the elicitin protein and tested its ability to change leaf physiological parameters of beech and tobacco plants. P. citricola produced a single acidic elicitin (citricolin), which caused necrosis and decreased gas exchange of tobacco leaves. Furthermore, it induced an oxidative burst in tobacco cell suspension culture. However, none of these effects were observed in beech.

Algal Proteins↗
PubMed1985

Relationship between Rapid, Firm Adhesion and Long-Term Colonization of Roots by Bacteria.

For rhizobacteria to exert physiological effects on plant growth, the bacteria must first effectively colonize the root surface. To examine the relationship between long-term colonization of root systems and adherence to roots in the short term, a binding assay was developed. Adherence was determined by incubating roots of intact radish seedlings with bacteria, washing and homogenizing the roots, and dilution plating the resulting homogenate. Irreversible binding of bacteria was rapid, reaching half-maximum by 5 min. All of the rhizosphere bacteria tested showed similar, concentration-dependent binding (ranging from 10 to 10 CFU/ml), as well as long-term colonization of radish roots under sterile conditions. Escherichia coli, which is not a root colonizer, showed about 10-fold less binding, but still demonstrated concentration-dependent binding and rapid kinetics of adherence at high concentrations (10 to 10 CFU/ml). The bacteria tested were very different with respect to source or habitat and plant response, yet they showed similar concentration-dependent binding. There was no correlation between the relative hydrophobicities of the cell surfaces of strains and the adherence of the strains to roots. Binding of Pseudomonas fluorescens E6-22 was promoted by divalent cations (Ca and Mg) at concentrations of 5 to 10 mM, whereas monovalent cations (Na and K) had little effect; electrostatic phenomena may partially explain adherence in the short term, an important prelude to long-term colonization of root surfaces.

Journal Article↗
PubMed2002

Ectomycorrhizal symbiosis can enhance plant nutrition through improved access to discrete organic nutrient patches of high resource quality.

It is known that roots can respond to patches of fertility; however, root proliferation is often too slow to exploit resources fully, and organic nutrient patches may be broken down and leached, immobilized or chemically fixed before they are invaded by the root system. The ability of fungal hyphae to exploit resource patches is far greater than that of roots due to their innate physiological and morphological plasticity, which allows comprehensive exploration and rapid colonization of resource patches in soils. The fungal symbionts of ectomycorrhizal plants excrete significant quantities of enzymes such as chitinases, phosphatases and proteases. These might allow the organic residue to be tapped directly for nutrients such as N and P. Pot experiments conducted with nutrient-stressed ectomycorrhizal and control willow plants showed that when high quality organic nutrient patches were added, they were colonized rapidly by the ectomycorrhizal mycelium. These established willows (0.5 m tall) were colonized by Hebeloma syrjense P. Karst. for 1 year prior to nutrient patch addition. Within days after patch addition, colour changes in the leaves of the mycorrhizal plants (reflecting improved nutrition) were apparent, and after I month the concentration of N and P in the foliage of mycorrhizal plants was significantly greater than that in non-mycorrhizal plants subject to the same nutrient addition. It seems likely that the mycorrhizal plants were able to compete effectively with the wider soil microbiota and tap directly into the high quality organic resource patch via their extra-radical mycelium. We hypothesize that ectomycorrhizal plants may reclaim some of the N and P invested in seed production by direct recycling from failed seeds in the soil. The rapid exploitation of similar discrete, transient, high-quality nutrient patches may have led to underestimations when determining the nutritional benefits of ectomycorrhizal colonization.

Chlorophyll↗
PubMed1983

Recent advances in hyaline membrane disease.

Survival of infants with HMD has improved remarkably in the last decade. This has resulted from improved methods of diagnosis, which enables clinicians to recognize infection, the patent ductus, and the presence of pulmonary hypertension complicating HMD; from improved methods of ventilation, which result in a lower incidence of acute and chronic complications; and from a reduced incidence of pulmonary and extrapulmonary complications, such as bronchopulmonary dysplasia and retrolental fibroplasia. These advances arise from a deep understanding of pulmonary and metabolic physiology of the newborn infant with respiratory distress. Only an approach firmly rooted in an understanding of physiology, pharmacology, and biochemistry can be completely successful in the therapy of these infants.

Anti-Bacterial Agents↗
PubMed1985

Cellular interactions at the central and peripheral terminals of primary sensory neurons.

Primary sensory neurons in the dorsal root ganglion play a fundamental role in the transmission of somatosensory information to the spinal cord and may also contribute to the neural regulation of inflammatory and immune responses in the periphery. Three aspects of the physiologic and molecular properties of dorsal root ganglion neurons require further analysis: a) characterization of the molecular events that regulate the differentiation of sensory neuroblasts into different functional classes of neurons; b) determination of the molecular basis for the specificity of central and peripheral connections formed by functional subsets of sensory neurons; c) identification of the chemical mediators released by the central and peripheral terminals of dorsal root ganglion neurons. Physiological studies indicate that excitatory amino acids, peptides, and possibly, nucleotides are released from primary sensory neurons and mediate both fast and slow synaptic responses in the dorsal horn of the spinal cord. Peptides and nucleotides have also been shown to regulate local blood flow and capillary permeability at the peripheral terminals of the sensory neuron. Cell surface carbohydrate differentiation antigens that delineate functional subsets of dorsal root ganglion neurons have recently been identified with monoclonal antibodies. The two major classes of dorsal root ganglion neurons that convey cutaneous sensory information express globo- and lactoseries carbohydrates. These carbohydrate structures have been implicated in intercellular adhesion and cell transformation in embryonic development and may be involved in cell recognition in the developing spinal cord. The identification of carbohydrate differentiation antigens will also be useful in analyzing the early lineage and development of sensory neurons.

Adenosine Triphosphate↗
PubMed2006

Analysis of quantitative interactions between two species of arbuscular mycorrhizal fungi, Glomus mosseae and G. intraradices, by real-time PCR.

Arbuscular mycorrhizal fungi (AMF) are obligate biotrophs, known to play an important role in ecological processes. Conventional light microscopy is the most common method used to detect their presence in planta, but this method fails to discern the presence of multiple AMF species and is not quantitative. These two factors are critically important in ecological studies, where the symbiotic contribution of each isolate needs to be defined. This paper describes the use of quantitative real-time PCR (qRT-PCR) as a detection system to address this issue. We used two Glomus spp., namely, G. intraradices and G. mosseae, to show that it is possible to study the interactions between these two isolates during the cocolonization of a single root system. Three different physiological studies were set up to assess how the interactions affected the occupancy of these fungi intraradically on a temporal basis. These treatments included saline and phosphorus stress, spatial distribution in the root zone, and preference for a particular host. qRT-PCR could prove a valuable tool in the area of AMF field ecology, where such data are critically important for defining the role of each species in the community structure.

Ascomycota↗
PubMed1990

The contribution of the dorsal and ventral roots of the tibial nerve in the propagation of the spinal somatosensory evoked potential in cats.

This study employed selective unilateral dorsal and ventral rhizotomy to examine the contribution of both the dorsal and ventral roots of the tibial nerve in the induction of the spinal somatosensory evoked potential (SSEP) in the cat. The spinal roots of origin of the tibial nerve in the cat were determined by retrograde transport of horseradish peroxidase (HRP). Spinal roots L6, L7, and S1 were found to give rise to the cat tibial nerve. Physiologic monitoring showed that the dorsal roots at these levels primarily contribute to the induction of the SSEP, but the ventral roots also make a small contribution. Because bilateral tibial nerve stimulation was found to mask a root injury on one side, we recommend sequential unilateral peripheral nerve stimulation when using SSEP during operations on the spine.

Animals↗
PubMed1994

Physiological, biochemical and molecular processes associated with gravitropism in roots of maize.

This research aims to characterize regulation of the principal cytosolic protein kinases in maize, cultivar 'Merit' root tips, since much evidence indicates that stimuli which modulate the gravitropic response in this system act through regulation of activity of these enzymes. To this end, we have cloned a maize protein kinase belonging to a group of plant protein kinases with a catalytic domain similar in primary structure to the second messenger-regulated protein kinases known in animal and fungal systems. However, both the unique structural features conserved among plant protein kinases in this group, and lack of evidence for cyclic nucleotide signalling in plants point to operation of a novel protein kinase regulatory mechanism in plants. In order to test effects of possible regulators on protein kinase activity, we developed a sensitive method for detecting regulation of autophosphoryl labelling of protein kinases in unfractionated maize protein extracts. Regulation of protein kinase autophosphorylation in these extracts was different from that known in animals and fungi, further suggesting operation of unique protein kinase regulatory mechanisms in plants. Previous research has shown that light, or factors modulated by light, regulate plant protein kinase activity. We found that protein kinase activity was co-immunoprecipitated with the plant photoreceptor phytochrome, and was associated with phytochrome by high-affinity chemical interactions. Far-red reversibility of red-light regulation of phytochrome phosphorylation by the associated protein kinase indicates that it may modulate or transduce the light signals which lead to gravitropic sensitivity in 'Merit' maize.

Calcium↗
PubMed1989

[Effect of epidermal growth factor (EGF) on proliferation of the cells derived from the root resorbing tissue of human deciduous teeth].

The resorption of the roots of deciduous teeth is a physiological phenomenon. Many morphological and histological investigations of the root resorption have been reported. However little biochemical data concerning systemic factors in it are available. In this study, cell culture derived from the root resorbing tissue of human deciduous teeth was tried and the effect of EGF on that cell was examined. The dissected root resorbing tissue from human deciduous teeth was cultured in a medium containing 10% fetal calf serum in a humidified incubator at an atmosphere of 5% CO2 in air at 37 degrees C. The outgrowing cells from root resorbing tissue were a mixed population of mesenchymal cells and epithelial cells during the early stage of cultivation, but at the later stage they changed to morphologically single population. The mesenchymal cells seemed to be derived from the dental sac and the epithelial cells from the enamel organ or the oral mucoepithelium. These cells seemed to be useful for analysis of the systemic factors in the root resorption. The effect of EGF on the proliferation of cells obtained as stated above was examined. EGF markedly stimulated DNA synthesis about by a factor of 6.9 for the mesenchymal cells and by a factor of 3.4 for the epithelial cells. These results suggested that EGF participates in the root resorption of human deciduous teeth.

Epidermal Growth Factor↗